Project Summary Glomerular dysfunction is a leading cause of the proteinuric kidney disease. It accounts for >90% of end stage renal disease (ESRD) cases, costing >$20B for treatment in the US alone. Currently, proteinuric kidney disease is treated with drugs, such as anti-hypertensives, that are systemically active to temporarily relieve the symptoms. Podocytes are essential for the formation of the glomerular filter. Because podocyte injury is an early event in the pathogenesis of various proteinuric kidney diseases, such as focal segmental glomerulosclerosis (FSGS) and diabetic nephropathy (DN), these cells are an excellent target for the development of targeted therapeutics. However, efforts for the rational development of podocyte-directed therapeutics have been hampered by the absence of any quantitative cell-based screening assay. Moreover, while many specific genetic abnormalities and environmental factors behind podocyte injury in patients have been identified, translation of such mechanistic insights into drug discovery efforts is sorely lacking. Recently, we have made significant progress in addressing these challenges (presented as preliminary data in the proposal), which includes ? a) development of a novel podocyte cell-based high throughput screening (HTS) assay and using it to identify 24 novel hits that protect podocytes from damage in vitro and in vivo; b) demonstration that our podocyte assay can accurately and reproducibly measure podocyte injury from patient-derived sera or in podocytes carrying patient-specific genetic defects, and showing that the genetic defects can be rescued via novel small molecules in knock-in animal models; and c) development of a novel humanized mouse model of proteinuric kidney disease, which can be used to validate novel hit compounds for faster translation into clinic. These exciting findings form the basis of our current proposal. We hypothesize that our novel podocyte-based screening assay could be used to discover novel candidate drugs that directly act on podocytes in patient-relevant settings. We further propose medicinal chemistry based optimization of confirmed hits. Furthermore, we hypothesize that adaptation of human podocytes with patient sera in this assay system will allow us to identify unique podo-protective compounds. Finally, we also hypothesize that inclusion of a humanized mouse model of kidney injury will provide us an improved in vivo model for hit validation so that we can rapidly nominate drug candidates for development into therapeutics for human patients in the future. We also propose an independent, in vivo validation of our hits. Our long-term goal is to develop novel therapeutic agents that target and stabilize podocytes as a strategy for the treatment of proteinuric kidney disease.